The analysis of objects using transmission electron microscopes (TEM) is an important method of analysis in the field of material science and in particular for the manufacturing of miniaturized objects, such as semiconductor devices. In order to analyze an object using a transmission electron microscope, a sample appropriate for being transmitted by an electron beam is prepared from the object. Such samples typically have a sheet-like shape with a thickness of less than, for example, 2 micrometer and are referred to as TEM-lamellae.
If a region of interest of an object is to be analyzed using the transmission electron microscope, a typical task is to prepare out a TEM-lamella from a substrate material of the object so that the region of interest is at least partially contained within the TEM-lamella. For this, material is conventionally removed by ion beam processing on both sides of a stripe disposed on the surface of the substrate above the region of interest and having a width of, for example, 5 micrometer, so that substrate material remains underneath the stripe, wherein the substrate material forms the TEM-lamella later on. Then, a tool is fastened to the stripe and more substrate material is removed until a material plate is fully cut free from the residual substrate. The material plate can be moved away from the substrate by using the tool. The material plate fastened to the tool may then further be thinned to finally form the TEM-lamella.
For preparing out a TEM-lamella from a substrate material, a particle beam system is often used including an ion beam column and an electron microscope (SEM) detecting secondary electrons, wherein the ion beam generated by the ion beam column for processing the substrate and the electron beam generated by the electron microscope for generating electron microscopic images of the substrate may be directed onto a common working area so that progress of the processing using the ion beam may be monitored by using the electron microscope.
For removing the substrate material on both sides of the stripe, an ion beam is directed onto those regions of the substrate from which material is to be removed. As the ion beam used thereto does not provide a sharply defined beam cross-section having, for example, a Gaussian intensity profile, ions also hit the stripe and penetrate into the region of the substrate forming the lamella later on and containing the region of interest. This region of the substrate is modified by the impinging ions so that the structure of the material in the region of interest is adulterated and might not be determined correctly by the subsequent analysis using the transmission electron microscope.
Therefore, a sufficiently thick protective layer of, for example, a metal is conventionally deposited on the stripe prior to the removing of material using the ion beam on both sides of the stripe, wherein the protective layer prevents the ions from penetrating into the substrate during the removing of the substrate material on both sides of the stripe.
Such protective layers are conventionally deposited from the gaseous phase, wherein the depositing is induced by irradiating the stripe using at least one of electron beams and ion beams.
The depositing of such protective stripes is elaborate and, in particular, the depositing from the gaseous phase involves specific technical equipment and influences subsequent processing steps to be executed in a high vacuum.